Ultrasulfophosphoric acids



Sept. 5, 1967 E. CSENDES ETAL 3,349,065

ULTRASULFOPHOSPHORIC AG IDS Filed July 17, 1965 4 Sheets-Sheet 1 INVENTORS;

ERNEST CSENDES WILLIAM R. MUS'HAN, JR.

ATT 'Ys p 5, 1967 E. CSENDES ETAL ULTRASULFOPHOSPHORIC ACIDS Filed July 17 1963 4 Sheets-Sheet 2 Om Ob 'IVLOJ. 9

nlsuoz N OE INVENTORS: ERNEST CSENDES WiLLIAM R. MUSTIAN, JR. BY

T'Ys

Sept? 5, 1967 E. CSENDES ETAL 3,340,005

ULTRASULFOPHOSPHORIC ACIDS Filed July l7, 1963 4 Sheets-Sheet 3 ORTHO @TRIPOLY T ETR A POLY ETC.

NORMAL MIGRATION PATTERN ORTHO 'PYRO 'TRIPOLY TETRAPOLY ETC.

SOLUBILITY FRACTIONATION PATTERN INVENTORS: ERNEST CSENDES WILEIIAM R. MUSTIAN, JR-

ATT'YS United States Patent 3,340,005 ULTRASULFOPHOSPHORIC ACIDS Ernest Csendes, Atlanta, Ga., and William R. Mustian, Jr., Lakeland, Fla., assignors to Armour and Company, Chicago, 11]., a corporation of Delaware Filed July 17, 1963, Ser. No. 295,647 6 Claims. (Cl. 23139) This invention relates to ultrasulfophosphoric acids having a phosphorus content of from about 83 weight percent (expressed as P 0 equivalent on an impurityfree basis) to a weight percent up to about 100 percent as P 0 equivalent on an impurity-free basis, said acids being liquid at ambient or room temperatures.

The importance of wet process high phosphorus con tent acids has been recognized by the phosphate industry for many years, but the results of the work in this field have been limited to acid products having a P 0 content on an impurity-free basis not substantially greater than 80 percent, and the workers in the field have warned against an increase in concentration on the ground that the product would become highly viscous and would be solid at ambient temperatures. The formation of metaphosphoric acid, which is undersirable for many reasons, was further set out as an objection to the production of a wet process phosphoric acid having a concentration beyond the previously-accepted concentrations.

The term superphosphoric acid (generally referred to as SPA) has been applied to wet process phosphoric acids having a weight percent of about 70 to about 80 expressed as P 0 equivalent on an impurity-free basis. Wet process acids above about 80 weight percent and, more specifically, about 83 weight percent and above, are designated ultraphosphoric acids (referred to herein as UPA), and such acids normally remain liquid up to a concentration of about 98 weight percent P 0 equivalent on an impurity-free basis.

We have now produced ultraphosphoric acids which remain liquid up to a weight percent of about 100 and higher, expressed as P 0 equivalent on an impurity-free basis and in which S0 is incorporated into the phosphoric acid compositions to form a new compound having important and surprising properties. Such an acid composition containing added S0 and having about 83 to about 100 weight percent and higher as P 0 equivalent on an impurity-free basis is referred to herein as wet process ultrasulfophosphoric acid or as USPA.

The S0 is preferably added as H 80 to the wet process phosphoric acid, but since the acid mixture is subjected to dehydration and since wet process phosphoric acid, which is produced by treatment of phosphate rock with H 80 normally contains a small amount of S0 it is believed that the addition of the sulphur group can best be expressed as added or excess S0 or, alternatively, as total S0 We have discovered that the addition of relatively small amounts of S0,; to the wet process acid, which is then subjected to high temperature quench reactions as described heerinafter, causes at least some of the S0 to enter into the ultraphosphoric acid lattice to form the new compounds which we have referred to above as ultrasulfophosphoric acids. The ultrasulfophosphoric acids are unique in that the reacted sulphur group (S0 is bound and does not react with ammonia or respond to ammoniation. Attempts to ammoniate the sulphur 3,340,005 Patented Sept. 5, 1967 group in the ultrasulfophosphoric acid compositions have been unsuccessful; while the phosphoric group ammoniates stoichiometrically, the sulphur group is ont ammoniated at all. Other test results are set out hereinafter which show unique characteristics in the reaction product.

It further appears that While wet process ultraphosphoric acid without added is characterized by a substantial drop in viscosity as the acid is concentrated above about 83 weight percent, such a drop or decrease in viscosity is not present in the ultrasulfophosphoric acid composition, but instead the ultrasulfophosphoric product has a substantially uniform viscosity profile.

In preparing the new product, the addition of S0 to the wet process acid has been found to reduce very substantially the temperatures required for converting the acid into the ultraphosphoric acid product. In some instances, the temperature requirement for conversion of the wet process acid to an ultraphosphoric acid of a selected Weight percent is lower by as much as F. when S0 is added to the wet process acid. Finally, the addition of the S0 to the wet process acid undergoing dehydration has resulted in an increased conversion of the orthophosphoric acid to the ultraphosphoric acids. The invention may be employed with all phosphoric acids of commerce, including wet process phosphoric acids and phosphoric acids made by other processes.

The high P 0 values of the ultrasulfophosphoric acid product may possibly be accounted for by the presence of known or unknown high phosphorus content compounds having values greater than 100 percent expressed as P 0 equivalent on an impurity-free basis, and the presence of S0 may be a substantial factor in the production of such compounds under the conditions of the process. In a process employing a pool of phosphoric acid subjected to submerged gas heating, a quench reaction apparently takes place wherein P 0 P 0, or other lower oxides of phosphorus are formed in the contact zone of hot gas and liquid acids. In turn, these species of phosphorus are chemically reactive at the temperatures employed in this process and may modify any metaphosphoric acid, trior tetrapolyphosphoric acid, or other phosphorus compounds, to yield our very high analysis ultraphosphoric acids. The presence of condensed molecules derived from P 0, or other like species with a high analysis in excess of percent P 0 equivalent, would thus substantially increase the P 0 content of acids in which they are present.

A primary object of the present invention is to provide new compounds or compositions having unusual properties, as described above. A further object is to provide a process for converting wet process phosphoric acid material into high P 0 equivalent phosphoric acids. A still further object is to provide novel means and process steps for improving the manufacture of phosphoric acids. Other specific objects and advantages will appear as the specification proceeds.

The invention is shown, in an illustrative embodiment, by the accompanying drawings, in Which- FIG. 1 is a side view in elevation, and partly in section, of apparatus illustrating our invention; FIG. 2, a graph setting forth conversion curves based on the addition of varying amounts of S0 FIG. 3, a paper chromatograph showing the normal phosphoric acid migration pattern when developed in basic and acid solvents; FIG. 4, a view similar to FIG. 3 but showing the migration pattern of our ultrasulfophosphoric acids; and FIG. 5, a graph showing the ratio of non-ortho conversion to 80;; in the final product and the relation of this ratio to the non-ortho P equivalent values of the products.

In one embodiment of our invention, we add sulphuric acid to wet process phosphoric acid and supply the combined acids to an evaporator to provide a pool therein. The acid pool is maintained at a desired temperature by submerged gas heating, the gaseous products of combustion being directed into the pool and the volume of the combustion gas being maintained at a substantially constant level. The temperature of the pool of acid is maintained at a selected temperature, plus or minus a few degrees, within a range of about 450 F. to about 650 F. For ultrasulfophosphoric acid, we may select a temperature in the range of about 450 F. to 650 F., yielding an acid product of about 83 to about 100 weight percent P O equivalent on an impurity-free basis and being liquid at ambient or room temperatures.

The desired pool temperature may be maintained by regulating the feed rate of fresh acid into the pool and by allowing the concentrated acid to overflow into a receiver vessel. By providing a system in which the acids are retained in the evaporator a relatively short time, we find that we can produce a uniform ultrasulfophosphoric acid in which the undesirable meta form is held to a low level and which contains about 83 to 100 and higher weight percent phosphorus, expressed as P 0 equivalent on an impurity-free basis.

While the acid starting material may be any phosphoric acid of commerce, we prefer to use the ordinary wet process phosphoric acid as the feed. Such acid usually has a metal oxide impurity content of from 1 percent to percent, but sometimes the metal impurities are as high as percent or more. For supplying heat to the process, we may provide a stream of hot gases resulting from combustion of air and fuel, such as propane or other gaseous or liquid fuels. The combustion gases may be tempered with outside air to bring the temperature of the gases discharged into the pool of acid to about 1500 F. to 1900 F. The gases fed to the evaporator are maintained at a constant rate irrespective of back pressures created in the evaporator by utilizing a combination of instruments or devices which will be described in greater detail hereinafter.

By way of specific illustration, wet process phosphoric acid, which may be of the range 27 to 64 weight percent phosphorus calculated as P 0 equivalent and to which sulphuric acid has been added, is pumped from feed tank 10, as shown in FIG. 1 of the drawings, through pipe 10a to evaporator 11, forming a pool in the frustoconical portion of the evaporator 11.

The hot combustion gases are directed through the dip pipe 12 to the lower portion of the reaction chamber where they are discharged from the lower inclined opening of the dip pipe. The gases discharged from the dip pipe proceed toward the bottom and an inclined wall of the frusto-conical portion. Here the swiftly moving stream of hot gases engages the liquid acids in the pool at the bottom of the evaporator arid while in intimate mixture with the acids carry them upwards in a state of turbulence within the reaction chamber. The moistureladen gases which disengage from the acid in the space above the evaporator bottom are removed by duct 13 to separator 14. Entrained a-cid droplets removed in the separator 14 are returned to receiver 21, and the gases continue on to the floating-bed scrubber 15, where condensable and water-soluble pollutants are removed.

The temperature of the liquid acids within the reaction chamber is maintained at a substantially constant value by a control circuit. The filled bulb 16 communicates with the pneumatic transmitter 17 through conduit 16a, and the pressure transmitter 17 communicates similarly through conduit 17a with the recorder'controller 18 which is pre-set to the desired temperature and which pneumatically operates through conduit 18a the diaphragm control valve 19 in the feed acid line 10a. In operation, the filled bulb 16 senses the acid temperature and records the same by means of transmitter 17 with recordercontroller 18 which is pre-set to the desired temperature, the signal from the bulb to the transmitter being by pressure through the gas-filled conduit 16a. The recorder-controller in operation adjusts the diaphragm control valve 19 so as to increase or decrease the amount of feed as required to maintain the set or predetermined temperature. The effect of this system is to decrease the feed rate with increasing water content of the feed acid, and to increase the feed rate when the water content of the acid decreases.

The dehydrated acid product is removed from the evaporator 11 through liquid overflow line 20, which is cooled by a water jacket 20a, to the receiving tank 21 Which is provided with a cooling jacket 21a. From the receiver 21, the product is passed by pump 22 to the product tank 23.

A fuel gas, such as propane, is passed from fuel tank 24 through conduit 25 to the vortex burner 26 where it is mixed with air (preferably an excess of air) from blower 27. Combustion takes place within the chamber 28, and the combustion gases are delivered through the dip pipe 12, as heretofore described. Overflow pipe 20 is located at a point on the evaporator, which is generally in line with the top of the liquid pool and which is opposite the inclined wall toward which the hot gases are directed.

A substantially constant rate of fuel gas input is maintained, irrespective of fluctuations in back pressure, by the following combination of control elements. A differential pressure meter 29 has a diaphragm 29a. Pressure conduits 29b and 290 lead to tapped openings communicating with the interior of the conduit 25 on opposite sides of a flow element 30 which is equipped with a disk or plate 30a providing a sharp-edged flow orifice. The conduits 29b and 290 are connected across the diaphragm 29a of the differential pressure meter 29 which measures the flow incident through flow element 30. The gas flows through the element 30 and is reduced in pressure by the balanced regulator 31, for example, to about 30" Water column. The differential pressure result is transmitted by element 29 to the recorder-controller 32 through pneumatic tube 221:. The controller 32 is provided with a control member which is pre-set to a selected pressure and therefore it responds to changes in flow of the fuel gas through flow element 30. For example, if there is an increased back pressure in the evaporator dip pipe, such increase is sensed by the conduit 23!) at one side of the orifice plate 30a, and such increase of pressure is transmitted through the transmitter 29 to the controller 32, which pressure, being above that to which the recorder 32 is set, causes the recorder to move the diaphragm control valve 33 toward open position. Similarly, with a decrease in back pressure, the recorder-controller 32 moves the diaphragm-controlled valve 33 a proportional distance toward closed position.

The S0 is added to the phosphoric acid preferably in the form of H 50 1 percent of Which provides a weight equivalent of .815 of S0 The addition of S0 to the phosphoric acid may be varied depending upon the amount of S0 already present in the feed acid, the volume of the pool of acid subjected to dehydration, the desired characteristics of the final product with respect to P 0 values, and other characteristics. Wet process phosphoric acid normally contains about 2.5 percent to 4 percent of S0 the average content being about 3.5 percent. We prefer to add enough S0 to bring the total S0 content of the acid undergoing treatment to about 6 percent to 11 percent. Under some conditions, the total S0 might be slightly reduced to about 5.5 percent, and with the percentage of the S increased above 11 percent, we find no advantages flowing therefrom. Best results have been obtained when the total S0 was in the range of about 7 percent to 9 percent.

The shift in conversion of the orthophosphoric acid in wet process phosphoric acid by reason of the adding of S0 to a wet processacid having an S0 content of 3.5 and a metal salt content of about percent, is shown by the graph of FIG. 2. While the limit of conversion of the orthophosphoric acid to polyand ultraphosphoric acid, without the addition of S0 is about 75 percent, it is found that the addition of S0 can bring about the conversion of more than 91 per-cent of the orthophosphoric acid in the feed material to ultrasulfophosphoric acid.

In the operation of our process for producing ultrasulfophosphoric acids, it is important that certain features of the process be taken into account. Referring particularly to FIG. 1, the hot gases proceeding into the reaction chamber through tube 12 move quickly to near the bottom of the frusto-conical lower portion of the reaction chamber, there entering the liquid pool. From the bottom of this chamber, the very hot gases moving together with portions of the liquid pool are passed upwardly guided by the frusto-conical surface of the lower portion of the chamber and move about within the chamber in intimate contact with the liquid acids, thus to provide effective heat transfer.

We believe that the reaction of dehydration takes place especially fast where small droplets or portions of liquid are in direct contact with the hot gas, and that upon reaction, the product so formed may then come into contact with larger bodies of liquid so as to be quenched and brought back to the temperature of the liquid body. As the reaction takes place and the reaction products reach the outlet 20, these products pass off from the reaction chamber and are quickly cooled. The reaction is rapid and violent, and it is important that reaction products be quickly removed after being formed.

To provide for quick removal of the dehydrated acids from the reaction zone, the rate of introduction of feed acids should be related to the volume of the acids within the reaction zone so that the acids will be passed through the reaction chamber in a certain minimum time. We find it important to use an acid feed rate in volume per minute which is at least A of the volume of the liquid within the reaction chamber and preferably at least /5 of the liquid volume within the reaction chamber (the volume in each case should, of course, be counted in the same units). To provide a range, we recommend that the ratio between volume per minute of feed and volume of liquid within the reaction zone be from to /12. From the foregoing, it will be seen that with a contemplated feed rate of 4 gallons of wet process phosphoric acid per minute, the reaction chamber should be designed so as to contain from 8 to 48 gallons of acids which would provide an average retention time of the acids within the reaction chamber of 2 to 12 minutes.

By way of example, in structure such as shown in FIG. 1, a volume of gallons may be provided by the frustoconical bottom portion of the evaporator in which the cone is 10 inches high, with a diameter of 23 inches at the top of the cone and with the liquid draw-off pipe 20 at a point 10 inches above the flow bottom of the evap orator.

We find that the addition of S0 to the wet process acid feed, as described above, provides a greater latitude with respect to the retention time of the acid within the reaction chamber, as will be illustrated by example set out hereinafter and in which the evaportaion is carried on in a reaction chamber having a volume of 15 gallons. In such an arrangement, we find that the acid free rate in volume per minute may be from /2 of the volume of the liquid within the reaction chamber to of such volume, and the average retention time of the acids within the reaction chamber may be from 2 to 15 minutes. Even with such an arrangement, however, we prefer to provide an average retention time of 10 minutes or less.

The temperature attained by the liquid acids through contact with the hot gaseous products of combustion should preferably be the boiling point of the acid in the desired product composition which has the lowest boiling point. For example, if it is desired to produce a composition having a concentration of weight percent phosphorus calculated as P 0 equivalent on an impurity-free basis from a commercial wet process phosphoric acid containing about 1.5 percent of metal salts, the feed acid should be brought to a temperature of about 600 R, which is the boiling point of such composition.

While the preferred range of pool temperatures is from 450 to 650 F., higher temperatures up to 1000 F. may be employed, particularly where a liquid product is not required.

The hot gases are introduced into the reaction chamber at such a rate that the heat given oli by them to the liquid acid is sufficient to raise the acids within the reaction chamber to the temperature which is selected in accordance with the principles outlined above. This rate is maintained by the automatic devices already described. By controlling the flow of fuel gas at a uniform rate, the heat input is thus maintained at a uniform rate and therefore the acids are heated uniformly even though there be temporary clogging or stoppage of the inlet pipe or of the discharge opening of the pipe. The design of this pipe may be such as to provide an adequate internal cross section so that at the desired rate of gas flow, the velocity of the gas issuing from this pipe will not be so great as to blow the liquid acids from the entire bottom portion of the chamber and thus destroy the liquid pool.

In the design illustrated in FIG. 1, the median pool cross-sectional area (226.9 sq. in.) bears with the crosssectional area of the dip pipe (28.3 sq. in.) the ratio of 8 to 1. We prefer that the median pool cross-sectional area should bear a ratio to the cross-sectional area of the dip pipe of at least 5.5 to 1. We find that if ratios are maintained within the range specified above, combustion gas velocity rates are possible which are sufiiciently high for the necessary heat transfer, yet are low enough to preclude the blowing dry of the liquid pool.

Another feature of the embodiment of our invention illustrated in FIG. 1 is that the outlet 20 for withdrawing product from the reaction chamber is opposite the inclined surface toward which the inclined opening of the dip pipe is directed so that the greater turbulence of liquid and gases is on one side of the chamber and there is less likelihood that such turbulence will affect the pool near the point where product is withdrawn.

From the above discussion on the relationship between temperatures of the acids, the rate of introduction of fuel, and rate of introduction of feed acids, it will be apparent that the system may be designed for larger capacity by proportionately increasing the size of the reaction chamber, the rate of introduction of feed acids, and the rate of introduction of fuel gas in the hot gas mixture, desirably also with increase in the internal size of the dip pipe to avoid increasing velocity to the point where the pool might be blown out.

PRODUCTS The ultrasulfophosphoric acid products may be defined in terms of P 0 equivalent either on an analysis basis or on an impurity-free calculated basis. In actual phosphoric acid plant practice, the products are analyzed on a 100 percent sample basis employing a standard procedure in which ammonium phospho molybdate is made from the phosphorus sample, and a volumetric determination of the phosphate P 0 values made by titration. Such a standard procedure yields a phosphoric acid product which is of lower numerical value than the corresponding calculated P 0 value of the product as on an impurity-free basis. By way of illustration, assuming that by the analy- Analysis, percent Irnpurity-Free Basis, Percent Conversion of percent Polyphosphoric Acids Paper chromatography in conjunction with solubility of fractionation shows that unique structures exist in our ultrasulfophosphoric acids. The solubility fractionation is carried out as follows:

The ultrasulfophosphoric acid is diluted and neutralized with NaOH solution at a temperature below 25 C. Solids are removed by filtration or decantation. The liquid portion which contains around 90% or more of the phosphate is treated with successive additions of a poor solvent, acetone, in amoutns sufiicient to precipitate a fraction of the phosphates. On addition of the solvent, a cloudy precipitation of a viscous immiscible liquid occurs. The mixture is stirred for several minutes and settled. The heavy gelatinous liquid settles to the bottom and is easily removed by decantation. The lighter decantate is saved for further fractionations. Approximately 2 parts solvent per part of sample are used in the initial fractionation. The amounts are increased for each subsequent fraction up to 2 parts solvent to 1 part sample. Up to -7 fractions are separated.

The fractions are then analyzed by paper chromatography and pH titrations. The first fractions have consistently given unique patterns on the chromatograms. The pH tit-rations show the first fraction contains chain phosphates with an average length of 3.5 P atoms. The chain length decreases in the subsequent fractions. The average chain length for the original acid ranges 2.2 to 2.5 P atoms.

The unique patterns of the first fraction on chromatograms are believed to contain the sulfophosphate structure. To verify the existence of sulfate in the first fraction, a dilute solution of BaCl is added to a diluted sample of the first fraction. The sulfophosphate structure is found to be relatively stable since no precipitation of BaSO occurs even after 1 hour digeston at boil. The presence of sulfate, however, can be confirmed by any one of three methods. The first is to digest the sample with a strong volatile acid to near d-ryness, redilute the sample, reacidify, dilute with water, and add BaCl Precipitation of BaSO occurs. This indicates the sample can be hydrolyzed to the individual constituents only by rather vigorous procedures. A second method for S0 detection is found by drying a sample of the first fraction for 18-24 hours at 70 C. under 26" Hg vacuum. Another test is made after approximately one week after the first fraction has been isolated. The sample is found to be hydrolyzed and BaCl additions will readily precipitate. BaSO Paper chromatograms indicate the sample undergoes hydrolysis during the two 24-hour migration periods. The papers show a predominance of ortho and pyro phosphates which have chain lengths less than that determined originally.

The acetone-precipitated fraction described above shows the linkage Similar precipitated fractions in our ultrasulfophosphoric acid products having 83 to 93 weight percent P 0 equivalent on an impurity-free basis showed the same characteristic linkage in which sulphur atoms are bonded to phosphorus atoms by intermediate oxygen atoms.

In the paper chromatography of our ultrasulophosphoric acids, two dimensional chromatograms are developed in a basic solvent, pH 10, consisting of propanol- 2, butanol-2 and NH OH; and an acid solvent, pH 2, consisting of propanol-2, trichloroacetic acid and NH OH. The solvent fronts travel perpendicular to each other. Ring compounds are more mobile in the basic solvent whereas chain compounds are more mobile in the acid solvent.

Rf values are measured by dividing the distance of solvent travel into the distance of spot travels. In our procedure, using 9" x 9" paper (S & S 589 orange ribbon), the solvent always travels the full length of the paper, i.e., 8". The phosphate sample is applied 1" from the bottom of the paper. This is the point at which measurements begin.

Normal migration patterns are shown in FIGURE 3 in which each species is labeled.

Solubility fractionations give a unique migration pat tern as shown in FIGURE 4. Table I compares the normal Rf values with R) values of solubility fractionations of USPA acids. The products of solubility fractionation are almost immobile in the basic solvent; and except for pyro, all have unique acid solvent Rf values. Another unique characteristic is the fact that all the species are connected by phosphates along the left vertical axis of the paper. As shown in FIGURE 4, the characteristic pattern is in the general shape of the letter F.

TABLE I.COMPARISON OF NORMAL Rf VALUES WITH SOLUBILITY FRACTIONATION RI Solubility Fractiona- Normal Values, tion Rfs Phosphate Species Rf, Acid Basic Basic Acid 28 68-. 73 19 20 42-. 48 13 43 18 21-. 33 09 20 Tetra Poly .15 11-. 22 06 09 Our ultrasulfophosphoric acids were also compared with ultraphosphoric acids to which excess sulphur is not added and with respect to the heat of dilution. In the following Table II, experimental derived values for the heat of dilution for UPA and USPA acids (on an analysis basis rather than an impurity-free basis) are set out.

FIG. 5 shows the diminishing ratio of the S0 to the non-ortho or poly-phosphoric acids as the latter increases. Some S0 is volatilized as the P 0 value of the acid rises, accompanied by an increase of the non-ortho acid components, and thus there is a definite falling off of the S0 content in proportion to the non-ortho content.

The new ultrasulfophosphoric acid product is less corrosive than the ordinary wet process phosphoric acid used as the starting material. It has a viscosity of from 2000- 9 5000 cps. at 100-125 B, being easily pumpable at these temperatures, and is non-corrosive in character, being suitable for handling in mild steel.

In the conversion to the higher total P values, such as 83-100 weight percent P 0 equivalent on an impurityfree basis, we find that the S0 reaches a rather constant percentage in the range of 0.8 to 3.5 percent in the final product. In the upper portion of this range of P 0 values, the S0 reaches a plateau in the range of 1-1.5 weight percent. It is indicated therefore that the above ranges of S0 are bound in the product molecule.

The S0 content in the final product may be substantial where the total P 0 is relatively low even though there is extensive conversion of the ortho to the polyphosphoric components, and such S0 may be in the range of 1 to 20 percent. The P 0 equivalent may be raised to 83 weightpercent or above on an impurity-free basis While yet yielding a product containing P 0 equivalent 0n the basis of the total composition of 76 weight percent or more. Thus we may produce a product with a P 0 equivalent of from 83 to 100 weight percent on an impurity-free basis with the S0 content reduced to from 3.5 to 0.8 weight percent and with a P 0 equivalent of 76 to 82. weight percent on the basis of the total composition.

The addition of the 50;, (in the form of H 80 from vessel 34 through pump 35 and metering device 36) to bring the total S0 content of the feed acid to about 7-11 percent was found to substantially reduce the citrate insolubility components of the product from about 10-11 percent without the addition of S0 to 5-6 percent when 50;, is added, a saving in the range of about 50 percent. Any such reduction inthe citrate insolubility of the product is of very substantial importance because citrate insoluble P 0 is not available to the plant.

The specific gravity of the USPA acids was about 2.2 (and within a range of 2.1 to 2.2), thus representing an increase of about 10 percent over the specific gravity of SPA acids which have a specific gravity of about 2.0. In terms of pounds, a gallon of SPA acid (72-80 weight percent on an impurity-free basis) would yield 12.1 pounds of P 0 while our USPA product (83-98 weight percent P 0 on an impurity-free basis) yields 14.5 pounds of P 0 In its simplest form, this reaction consists of the introduction of one mole of S0 in linear arrangement between two moles of orthophosphoric acid, resulting in the attendant loss of one mole of water from the respective active hydroxyl sites of the orthophosphoric acid molecules. This reaction is illustrated in structural form in the following equation:

Higher degrees of polymerization are also realized by the further substitution of S0 between the new molecules thus formed in the following manner:

Example I To wet process phosphoric acid containing 3.5 percent SO was added sulphuric acid (90* to 93 percent) to provide an additional 3.5 percent of 50;, in the acid feed. Theacid feed containing approximately 7 percent of 80;, was fed to a 10 gallon evaporator, as shown in FIG. 1, the feed having the following composition:

Percent S0 7.0 A1 0 1.5 F6203 Solids 2.4

Hot gases produced in the combustion chamber (using propane and air) were admitted to the evaporator at the temperature of 1750 F. and directed under the surface of the acid. The acid pool was maintained at a temperature of 600 F., plus or minus 2 F. Feed acid of the above composition was admitted at a rate of 1.5 gallons per minute. The average retention time was 10 minutes. The product Withdrawal rate w-as about 1.0 gallon per minute. The moisture laden gases, which disengaged in the space above the acid pool, were at about 675 F. and were removed through a duct to a cyclone separator. Aboutone percent of the product acid was recovered in the cyclone separator and returned to the product receiver. After removal of the entrained acid droplets, the gases continued to a floating-bed scrubber where condensable and water-soluble pollutants were removed. The eflluent gases issued from the stack of the floating-bed scrubber at a nil content of fluorine and S0 and about 2 lbs. .per day of S0 The product had the following composition:

Total,P O percent.. 100.0 Ortho, do.. 9.0 S0 do 9.0 F do 0.1 A1203 dfl F6203 -d0 3.3 CaO do 0.1" M'gO do 0.7 Solids dn 1.4 Specific gravity 2.18

Asindicated above, the conversion of ortho to ultrasulfophosphoric acid was 9 1 percent. The product had a viscosity of 13,000 cps. at F.

The control means for maintaining the temperature within a few degrees of the selected temperature was as follows: Propane gas was admitted through a conduit at about 30 p.s.i.g. The combination of control elements was as,

shown in FIG. 1 of the drawing. The gas flowed through the orifice of plate 30a and was reduced in pressure by the balanced regulator 31 to 30" Water column. The pressure taps around the flow plate 30a were connected across the diaphragm 29a of the differential pressure meter 29 (Foxbor-o Type 15A d/ p Cell Transmitter) for the purpose of measuring the flow incident through the element 30. The pressure dilferential result was communicated through the pneumatic pipe 32a to the recorder-controller 32, which was a series 500 proportional air-operated free-vane controller, Bristol Company instrument bulletin A1420. The control of the recorder-controller was set to respond to changes in flow of the propane gas through flow element 30. As the flow of gas varies, due to changing back pressure in the evaporator, a pneumatic signal is transmitted from controller 32 to the diaphragm control valve 33, which opens in response to an increase in back pressure, and which closes with a decrease in back pressure. This control provided a substantially constant volume of fuel gas throughout the operation. Air was supplied by blower 23 in excess of the amount needed for combustion. The combustion occurred in chamber 28, and gaseous products of combustion were discharged through pipe 12 into the pool of acid below the surface of the pool.

The temperature of the combustion gases discharged into the pool of acid was about 1750 F. With a constant heat input, it was necessary to control the input of feed acid so as to maintain a constant acid pool temperature or its corollary product composition. A filled bulb 16 in the acid pool transmitted the temperature result by pressure through a gas-filled conduit upon the pneumatic transmitter 17 which transmitted the result to recordercontroller 18. The pressure transmitter was Taylor Instrument Company Model 339R, and the recorder-transmitter was Taylor Instrument Company Fulscope Controller, the latter instrument being set for a predetermined acid pool temperature and it operated the diaphragm control valve 19 to decrease the feed rate when the feed acid had a high water content and to increase the feed rate proportionally as the water content of the acid decreased. A uniform pool temperature was obtained, plus or minus 2 F.

Example II The process was carried out as described in Example I, sulphuric acid being added to provide a total 50;, content in the feed acid of 6.2 percent by weight. The final proda uct contained the following:

The combustion gases entering the pool had a temperature of 1850 F. The acid pool temperature was 600 F. The volume of the acid pool was gallons. The acid feed rate was 1.7 gallons per minute. The retention time was 5.9 minutes. The product rate was 0.7 gallon per minute. The temperature of the product in the receiver was 450 The eflluent gas temperature was 680 F. The final product on an analysis basis was 79.1 weight percent and on an impurity-free basis was 87 weight percent. The ortho content was 8.40 percent, and the conversion to polyphosphoric acid was 89 percent.

Example III To feed material of the composition set out in Example I, except that it contained 13 percent solids, was added 1'2 sulphuric acid (90-93%) to provide an additional 5.5 percent of S0 in the feed acid. The feed acid containing approximately 9 percent of $0 was fed to a 10 gallon evaporator, as described in Example I. The operating conditions were maintained as described in Example ll except that the acid pool temperature was controlled at 580 F., plus or minus 2 F. The feed rate was 1.2 gallons per minute, and the retention time about 8 minutes. The product withdrawal rate was 0.8 gallon per minute. The effluent gas temperature was 650 F. The productreceiving temperature was 450 F. The temperature of the combustion gas entering the liquid pool was 1750 F.

The product had the following composition:

Percent P 0 91.0 Ortho 14.0 S0 9.5 F 0.3 Al O 1.5 Fegog CaO 0.1 MgO 0.6

Conversion of orthophosphoric acid to polysulfophosphoric acid was 81 percent.

The product was liquid at F., and had a specific gravity of 2.15. The control means for maintaining the temperature within a few degrees of the selected temperature was as described in Example I.

Example IV The process was carried out as described in Example I except that the solids in the wet process acid were 10 percent and the S0 content was raised to 13 percent. The combustion gas temperature entering the pool was 1750" F., and the acid pool temperature was maintained at 600 F., plus or minus 2 F. The acid feed rate was 1.1 gallons per minute, and the product withdrawal rate was 0.6 gallon per minute. The efiluent gas temperature was 675 F., and the retention time was 13.6 minutes.

The product had the following composition:

viscosity of 30,000 cps. at 80 F. The percent conversion to polysulfophosphoric acid was 89.0 percent.

Example V A series of runs designated as A, B, C, D, E, F and G in Table III below were carried out as described in Example I upon a feed product substantially as described therein, the feed composition being as follows:

Percent l1: 0 54.6 1.0 A1 0 1.5 F203 Solids 2.4 S0 3.5

Excess S0 was added to bring the total S0 content in the runs to the total contents indicated in Table III. The conditions of operation and final results are indicated in Table III:

TABLE III A B G D E F G Percent P10 86. 92. 0 93.0 92. 0 89. 0 87. 0 5. 1 9. 11.3 9. 2 9. 0 6. 0 0.1 0.1 0.1 0.1 0.1 0.1 1.7 1.8 1.7 1.8 1.7 1.8 1.5 1.7 1.7 1.7 1.7 1.5 0.1 0.1 0.1 0.1 0.1 0.1 0. 7 0. 7 0. 7 0. 7 0. 7 0. 7 9. 7 10. 6 11.5 10. 5 9. 0 5. 4 2. 18 2. 2. 20 2. 20 18 2. 20 1, 760 1, 700 1, 800 1, 800 1, 900 1, 850 660 640 620 600 570 610 10 10 10 10 10 10 1.4 1.3 1.5 1.5 1.5 1.7 Retention Time (min.)..-. 7.1 7. 6 6. 7 6. 7 6. 7 5. 9 Product Rate (g.p.m.). 0. 8 0. 7 0.8 0. 8 0.8 0. 7 Product Receiver F.) 450 450 450 450 450 450 Efliuent Gas Temp. F.) 710 700 680 670 650 680 Ortho in Final Product 18. 3 15. 8 17. 9 16. 2 20. 7 21. 0 Conversion to Poly (Non-Ortho)--. 77 82 80 81 75 75 SO; in Final Product 1. 4 1. 0 1. 3 1. 0 1. 8 1. 1

Example VI 3. The product as defined 1n claim 1 having the charac- A series of runs designated as H, I, J and K were 5 terized linkage 4. In a process for preparing ultrasulfophosphoric acid, the steps of adding to wet process phosphoric TABLE IV H I J K Percent Total P101 90.0 91.0 98.0 98. 0 Percent Ortho 27. 0 14. o 9. 0 9. 0 Percent S0,... 14. 0 11.0 15. 0 13. 0 Percent F---" 0. 4 0.3 0. 1 0.08 Percent A150. 1. 4 1. 5 2 2 2. 2 Percent F8103--- .2. 9 3. 1 3. 3 3. 3 Percent CaO.. 0.1 0.1 0.1 0.1 Percent Mg 0.6 0.6 0.7 0.8 Percent Solids... 10.0 13.0 1. 4 10.0 Specific Gravity... 2.13 2.15 2. 18 2.18 Combustion Gas 1, 750 1, 750 1, 750 1, 750 Acid Pool Temp. (7 F 500 580 600 600 Acid Pool Volume (gal. 15 15 15 15 Acid Feed Rate (g.p.m.). 1. 2 1. 2 1. 5 1.1 Retention Time (min.) 12. 5 12. 5 10.0 13.6 Product Rate (g.p.ru.) 0.8 0.8 1.0 0. 6 Product Receiver Temp. C F.). 450 450 450 450 Efliuent Gas Temp. 0 F.) 575 650 675 675 Percent Conversion to Polyphosphoric Acids.-- 62. 5 81.0 88.0 89. 0

acid containing 1-15 percent metal impurities to bring the total 80;; content to 6-11 weight percent, and dehydrating the same to a phosphorus content of 83-100 weight per- While in the foregoing specification we have set out cent expressed as P 0 equivalent on an impurity-free specific embodiments of the invention in considerable basis by heating to a temperature of about 450-650 F. detail for the purpose of illustrating the invention, it will 5. The process of claim 4 in which the combined wet be understood that such detail or details may be varied process phosphoric acid and 80;, are dehydrated until widely by those skilled in the art without departure from about 70-100 weight percent of the orthophosphoric acid the spirit and scope of our invention. is converted to polyphosphoric acid.

We claim: 6. A process for preparing wet process ultrasulfophos- 1. As a new composition of matter, wet process ultraphoric acid containing as impurities metal salts in the sulfophosphoric acid having a phosphorus content of amount of 1-15 Weight percent, comprising adding 80;, 83-100 weight percent expressed as P 0 equivalent on to said acid to bring the S0 content of said phosphoric an impurity-free basis, the sul-fo group being present as acid to about 55-11 weight percent, and passing a stream 80;; and having sulfur atoms bonded to phosphorus atoms of hot gases into contact with said liquid acids in a reby intermediate oxygen atoms. action chamber and through such contact bringing said 2. The product of claim 1 in which the S0 is bound acids to a temperature of about 450-650" F., introduc- SO and is present in the amount of 0.8-3.5 weight pering fresh acids into said chamber while controlling the cent. rate of introduction at a rate, measured in volume per 3,340,005 15 16 minute, which is at least of the volume of liquids in OTHER REFERENCES said chamber.

Van Wazer: Phosphorus and Its Compounds, vol. 1,

References Cited Interscience Publishers, Inc., New York, 1958, pages 708, UNITED STATES PATENTS 5 to 2,901,34O 8/1959 Semel et a1. 23-139 X 3,030,200 4/1962 Harris n; 23 139 X OSCAR R. VERTIZ, Primary Examiner. 3,104,947 9/1963 Switzer et a1. 23165 H. T. CARTER, Assistant Examiner.

3,192,013 6/1965 Young 23--165 

1. AS A NEW COMPOSITION OF MATTER, WET PROCESS ULTRASULFONPHOSPHORIC ACID HAVING A PHOSPHORUS CONTENT OF 83-100 WEIGHT PERCENT EXPRESSED AS P2O5 WQUICALENT ON AN IMPURITY-FREE BAISI, THE SULFO GROUP BEING PRESENT AS SO3 AND HAVING SULFUR ATOMS BONDED TO PHOSPHORUS ATOMS BY INTERMEDIATE OXYGEN ATOMS.
 4. IN A PROCESS FOR PREPARING ULTRASULFOPHOSPHORIC ACID, THE STEPS OF ADDING SO3 TO WET PROCESS PHOSPHORIC ACID CONTAINING 1-15 PERCENT METAL IMPURTIES TO BRING THE TOTAL SO3 CONTENT TO 6-11 WEIGHT PERCENT, AND DEHYDRATING THE SAME TO A PHOSPHORUS CONTENT OF 83-100 WEIGHT PERCENT EXPRESSED AS P2O5 EQUIVALENT ON AN IMPURITY-FREE BASIS BY HEATING TO A TEMPERATURE OF ABOUT 450-650*F. 